1. Technical Field
The present invention pertains to apparatus and methods for vehicular signaling and, in particular, to apparatus and methods by which a lead vehicle may emit a defensive signal for perception by a following vehicle
2. Description of Related Art
Rear end collisions (REC) impose a staggering burden on society. The total money cost arising from personal injuries, lost wages, employer productivity, and property damage is estimated to be between $5 billion and $10 billion in the U.S. alone. In 1996, the National Highway Traffic Safety Administration estimated that about that 28% of all accidents involve rear-end collisions between a lead vehicle (LV) and a follower vehicle (FV). Highway safety studies indicate that a rear-end crash has about a 67% chance of generating a reported whiplash injury. As a result, rear end collisions annually result in damage to over 1.5 million vehicles and, importantly, cause over one million cases of whiplash injury.
Modern highways worldwide seem to become more crowded each day, with many metropolitan areas enduring chronically congested roadways. Public transportation and freight vehicles, with generally greater physical dimensions and operating at lower average speeds, are intermixed with more maneuverable, smaller private vehicles. Operators of all vehicles feel pressures to meet itinerary deadlines, especially during peak travel times, often leading to compulsive tailgating, abrupt lane changes, sudden braking, and intemperate driving. All too often, a REC occurs when a following-vehicle operator (FVO) fails to timely recognize an abruptly slowing, or stopped, vehicle in the road ahead.
Because more than 75% of REC accidents occur during daylight hours, with 90% occurring on straight roadways, driver inattention is believed to be the primary factor in over two-thirds of these collisions. Following too closely, or “tailgating,” is thought to be the second most likely cause of REC. In nearly 90% of all REC, the imputed cause of the collision was one or both of inattention, tailgating, or both. A third major factor in REC is ambient lighting conditions. Poor lighting conditions reduces visual contrast and visibility, produces limited depth and motion perception, and demands longer periods of observation and processing of visual images.
Under reduced lighting, a vehicle operator typically takes longer to perceive, identify, and respond to a hazard, thereby reducing the time and distance available to take evasive measures. Some operators significantly misjudge the distance, motion, and size of objects in their path during dark hours, so that dark hour collisions tend to be preceded by less braking or evasion, and result in more forceful impacts. Surprising or unexpected operating situations may further increase an operator's response time, so that an unexpected hazard on a darkened road may elicit a fatally delay in the operator's response. Thus, for the 25% of REC that occurs during dark hours, the risk of severe injury or death trebles.
Attention, focus, and skilled responses are essential concomitants to any safe trip. However, these capabilities vary greatly among individuals. Some factors, such as operator age, bring both benefits and liabilities, with the experience and judicious vehicle handling exhibited by older drivers being a slight advantage over the sharp faculties and rapid reflexes of younger drivers.
Typically, an unimpaired driver exhibits a response latency of about 1.8 seconds, as measured from the moment the driver perceives a stimulus until the moment the driver reacts to the stimulus—but before the vehicle responds to the driver's actions. Under certain circumstances this response latency may be less; yet under others, such as with a distracted driver, response latency can be substantially greater. In the microcosm of rear-end vehicle accidents, a split-second makes the difference between a close-call and tragedy. For example, at a modest speed of about 30 mph (50 kph), a vehicle traverses approximately 85 feet (25 meters) during this response latency period, corresponding to nearly five-and-a-half car lengths of movement. At highway speeds of 55-70 MPH (88-100 kph), a 1.8 second delay translates into about 150-200 feet (44-60 meters) of movement. From a more familiar perspective, vehicles moving at speeds between 30 MPH and 70 MPH, move about one to three car lengths, i.e., 15-35 feet or 3-11 m in the blink of an eye.
For the most part, current vehicle safety research remains focused on devising apparatus and algorithms directed to collision avoidance and from the vantage of the FV operator (FVO), i.e., outfitting a vehicle in a defensive follower role (FV). In general, a FV safety system detects, and is responsive to, a sensed operational characteristic exhibited by a lead vehicle (LV), which is located at some distance ahead of the defensive follower vehicle (FV). One response of a FV safety system (hereafter, a collision avoidance system or CAS), is to produce a perceptible warning to the FVO, with the expectation that the perceived warning will be sufficiently timely for the FVO to avert or mitigate a rear end collision.
Common CAS tend to include, for example, systems based on forward-directed interrogation signals (e.g., RADAR) emitted by the FV, and reflected back to the FV from the LV. FV systems also may include ultrasonic, optical, and red-based forward position or zone analysis, radio geolocation and global positioning systems and devices, as well as any system or device disposed within a vehicle that performs forward-looking analysis of a LV characteristic. Haptic FV systems also are of recent interest because there is some indication that a CAS alert issued through contact with the operator's body (e.g., vibrating steering wheel or seat) may promptly elicit a desired response.
More complex and sophisticated CAS may not be desirable. In general, increasing the complexity of any system increases the likelihood of constituent component failure. While a sophisticated collision avoidance system may enhance the safety of vehicle occupants, its failure can nullify the advantages gained. Should the vehicle operator become lax in reliance on the CAS forewarning, a system failure may increase the operator's risk by offering a false sense of security.
By selectively adding redundancy to a CAS, a certain degree of failure can be accommodated, but redundant systems are frequently more complex, and costlier to purchase, operate, and maintain than their non-redundant counterparts. Moreover, some degree of error is inevitable in any system intended, by design, or by common usage, to serve as a surrogate for attentive, skilled human judgment, particularly in the unpredictable settings and environments that modern vehicles frequently encounter. Of course, a CAS can appreciably increase the cost of owning and maintaining a vehicle, which may be beyond the means of the average vehicle owner.
Despite extensive research and development into understanding vehicle and collision kinematics, human machine interfaces, and studies revealing a wide range of vehicle operator responses, collision avoidance systems lack widespread implementation or acceptance, ostensibly due to the significant complexity, cost, maintenance, interoperability, and reliability concerns, of vehicle manufacturers, public officials, and consumers alike.
In an attempt to provide an LV with additional visibility, automobiles in the United States have been equipped with central high mounted stop lamps (CHMSL). A CHMSL is typically positioned between, and vertically higher than the rear stop/brake lamps of a vehicle. Initially, the implementation of CHMSL seemed to account for a noticeable decrease in REC. However, over time, drivers appear to have become less responsive to this additional indication of the LV state. Indeed, a standard CHMSL does not provide more information to an FVO regarding the deceleration, or stationarity, of an LV. Traditional CHMSL indicate that the LV braking system has been activated, without offering unambiguous cues to an FVO regarding LV speed or deceleration. Moreover, it is now believed that CHMSL may not provide sufficient stimuli to seize the focus of an inattentive FVO, even as a supplement to the standard brake/stop lamping. It is desirable, therefore, to provide a simple, intuitive, relatively inexpensive vehicle signaling system that provides attention-alerting stimuli conducive to effecting rapid, accurate maneuvers by an FV driver, thereby avoiding or mitigating a rear-end collision.